Fibrous metal filaments



April 7, 1970 J. A. ROBERTS ET AL 3,505,039

FIBROUS METAL FILAMENTS Original Filed March 2, 1964 2 Sheets-Sheet 2 l/FATED DIES United States Patent 3,505,039 FIBROUS METAL FILAMENTS John A. Roberts, Chelmsford, and Peter R. Roberts,

Groton, Mass, assignors to Brunswick Corporation Original application Mar. 2, 1964, Ser. No. 348,326, now

Patent No. 3,394,213, dated July 23, 1968. Divided and this application July 2, 1968, Ser. No. 742,010

Int. Cl. B21c 37/04; B23p 3/10 US. Cl. 29-191.6 14 Claims ABSTRACT OF THE DISCLOSURE This application is a division of application Ser. No. 348,326, Mar. 2, 1964, now US. Letters Patent No. 3,394,213, July 23, 1968.

This invention relates to the forming of fine filaments and in particular to the forming of such filaments having very long lengths.

In the manufacture of material, such as reinforcing fabrics, filtering media, etc., there has developed a need for high strength metallic filaments. More specifically, it has been found that, in such materials, metallic filaments having extremely small diameters, such as under 15 microns, may provide increased tensile strength. Further, such small diameter filaments when formed in suitable pads provide improved filtering action. The present invention is concerned with the forming of such metal filaments and comprehends an improved method of forming, providing extremely long lengths of such filaments having a diameter of under 15 microns.

Thus, a principal feature of the present invention is to provide new and improved textured filaments.

Another feature of the invention is to provide fine filaments in extremely long lengths.

A further feature of the invention is to provide filaments having a diameter of down to approximately 12 microns or less in lengths of over 50,000 feet.

Another feature of the invention is to provide for utilizing metallic material surrounding the elements from which the filaments are formed with a high ratio of filament material to matrix material being employed.

Still another feature of the invention is to provide an economical filament.

A yet further feature of the invention is to provide a filament having a texture developed by hot and cold forming.

Another feature of the invention is to provide a filament wherein elements are constrictively reduced in crosssection while in a sheathing matrix material with the sheathing matrix substantially removed thereafter.

Another feature of the invention is to provide a filament with a controlled nonuniform cross-section by selectively hot and cold working the filament-matrix composite.

A further feature of the invention is to provide for such a composite having a preselected filament-matrix ratio.

Still another feature of the invention is to provide that the elements from which the filaments are formed are tubular with the resultant filaments comprising tubular filaments.

3,505,039 Patented Apr. 7, 1970 Yet another feature of the invention is to provide for a filler to be inserted into the tubular elements prior to hot and cold forming.

Another feature of the invention is to provide for a tow of metal filaments each having a maximum crosssection of approximately 12 microns and a length of greater than approximately 50,000 feet.

Still another feature of the invention is to provide for a tubular filament having a hexagonal cross-section.

Other features and advantages of the invention will be apparent from the following description taken in connection with the accompanying drawings wherein:

FIGURE 1 is a transverse cross-section of a metal wire from which a filament may be formed in following the method embodying the invention;

FIGURE 2 is a transverse cross-section of the wire disposed within a coaxial sheath as in a first step of the method;

FIGURE 3 is a perspective view of a plurality of sheathed wires disposed in a cylindrical housing in a subsequent step, the housing being broken away to illustrate the bottom portion thereof;

FIGURE 4 is a reduced vertical section of a compacting means illustrating a compaction of the assembly of sheathed wires in the cylindrical housing to define a compacted billet;

FIGURE 5 is a reduced vertical section of another form of compacting means illustrating another method of reducing the diameter of the assembly to define a compacted billet;

FIGURE 6 is a top plan view of a plurality of sheathed wires in a modified housing having a hexagonal internal cross-section as by the provision therein of sector shaped spacers;

FIGURE 7 is a top plan view of a modified arrangement of the sheathed elements in a cylindrical housing with spacers disposed between the sheathed elements to effectively minimize the voids therein;

FIGURE 8 is an exploded vertical section illustrating the arrangement of the housing subsequent to the installation of the sheathed wires therein and prior to the securing of the end plug across the open end thereof;

FIGURE 9 is a vertical section illustrating the arrangement of the sheathed wires in the housing with the end plug secured across the open end of the housing;

FIGURE 10 is a vertical section illustrating the step of evacuating and sealing of the housed sheathed wires to define the primary billet;

FIGURE 11 is a fragmentary diagrammatic elevation of the billet during a subsequent hot extrusion step;

FIGURE 12 is a diagrammatic elevation of the extruded billet with suitable cutting means acting to remove the opposite ends of the exruded bundle;

FIGURE 13 is a diagrammatic elevation illustrating the cutting of the extruded billet into a plurality of shorter lengths;

FIGURE 14 is an elevation of one of the short lengths being provided with a replacement plug at each of its opposite ends;

FIGURE 15 is a fragmentary side elevation of a short length being further hot extruded to reduce the diameter thereof;

FIGURE 16 is a side elevation of the original billet being reduced in diameter as by hot rolling means in lieu of or subsequent to the hot extrusion means of FIGURE 11;

FIGURE 17 is a fragmentary diagrammatic vertical section illustrating the cold drawing of the hot formed billet in a subsequent step;

FIGURE 18 is a vertical cross-section of a tank wherein the drawn billet of FIGURE 17 is disposed to be 3 acted upon by a suitable fiuid within the tank to remove the sheating and housing material from the billet;

FIGURE 19 is a resultant tow of filaments embodying the invention;

FIGURE 20 is a transverse cross-section of a metallic tubular element from which a tubular filament may be formed in accordance with the invention, a filler being disposed within the tubular element as in a first step of the method;

FIGURE 21 is a transverse cross-section of the filled tubular element disposed within a tubular sheath as in a second step of the method;

FIGURE 22 is a transverse cross-section thereof constricted to provide a tight assembly of the filler, tubular element, and sheath as in a third step of the method;

FIGURE 23 is a perspective top view of the filled and sheathed tubular elements disposed within a cylindrical housing for subsequent sealing, hot forming, and drawing steps as illustrated in FIGURES 7 through 17; and

FIGURE 24 is a fragmentary enlarged perspective view of a tubular filament formed by the method.

In the exemplary embodiment of the invention, a tow generally designated 10 of filaments 11, as shown in FIGURE 19, is formed by a process wherein a plurality of elongated elements, or wires, 12 are bundled in sideby-side relationship and, when so bundled, reduced in diameter by a transverse, or radial, constriction of the wires in the bundle to provide a resultant filament of extremely small diameter and great length. Alternatively, the invention comprehends the forming of the filament as a tubular filament 13, as shown in FIGURE 24, the original elongated element in this process comprising a tubular element 14, as shown in FIGURE 20.

Broadly, the invention comprehends the constriction of the bundled wires, or tubular elements, by firstly forming the bundled wires or elements into a billet, and subjecting the billet successively to a hot forming constriction and a subsequent drawing constriction. The hot forming constriction may be alternatively by hot extrusion or hot rolling of the billet. The drawing operation may comprise a plurality of cold drawing steps with intermediate annealing steps.

Referring now to FIGURES 1 and 2, the wire 12 is firstly enclosed in a suitable sheath 15 formed of a material having physical characteristics differing from those of the wire 12 to permit separation of the sheath material from the resultant filaments when desired. As illustrated in FIGURE 2, the original internal diameter of the sheath may be slightly larger than the external diameter of the wire 12 to permit facilitated insertion of the wire into the sheath. The thusly, loosely sheathed wires may then be installed in a can, or housing, 16 having a bottom closure wall, or nose plug, 17, with the sheathed wires extending in parallel side-by-side upright relationship, as shown in FIGURE 3.

For improved uniform constriction of the wires in the subsequently constricting steps, it is desirable to closely pack the sheathed wires within the housing 16 as by suitably compacting the assembly. Referring to FIGURE 4, one method of effecting the desired compaction is by placing the assembly in a press generally designed 18 having a liner 18a defining a cylindrical cavity closely fitting the cylindrical housing 16. The lower end of the cavity is closed by a blind die 18b and the liner 18a and blind die 18b are supported on a suitable anvil 180. A ram 18d is provided to apply pressure on the top of the assembly whereby the assembly is axially shortened and thereby laterally or radially compacted. Such compacting apparatuses are well known in the art and need no further description herein.

Turning now to FIGURE 5, an alternate method of effecting the desired compaction of the assembly is shown to comprise the compaction of the assembly by means of an extrusion apparatus generally designated 118. In apparatus 118 an extrusion die 118a is provided 4 through which the assembly is longitudinally forced by means of a suitable pressure applying element 118b. Only a small amount of constriction of the assembly is effected by die 118a so that only an elimination of the voids in the assembly is effected in this step.

Referring now to FIGURE 6, a method of facilitating the compaction of the assembly is illustrated. More specifically, the internal configuration of the housing 16 is made to be hexagonal in transverse cross-section by means of a plurality of spacers 19 comprising chordal sector pieces.

FIGURE 7 illustrates a further method of facilitating the compaction of the assembly. More specifically, in FIGURE 7 the sheathed wires 12 are shown installed within the housing 16 with a plurality of spacers, or suitable particulate materials such as metal powder 21 disposed between the wires. Thus, with the arrangements illustrated in FIGURES 6 and 7, less compaction of the assembly by the steps illustrated in FIGURES 4 and 5 is required to provide the desired compacted billet.

Prior to the compaction steps discussed above, the sheathed wires 12 are sealingly enclosed within the housing 16 by means of an end plug 23 installed across the open end 24 of the housing 16. As illustrated in FIG- URE 8 the end plug comprises a generally cylindrical disk having a notched portion 23a adapted to engage the upper end of the housing in the housing closing arrangement. The end plug 23 is further provided with an evacuation pipe 26 which opens through a central hole 231) in the end plug, being secured to the end plug by suitable means such as weld 26a.

With the sheathed wires 12 installed in the housing 16, as shown in FIGURE 10, the end plug 23 is secured across the open upper end 24 of the housing by suitable means such as weld 230. The evacuation pipe 26 is utilized during the welding of the end plug to the housing end 24 to flush the interior of the housing during the welding of the plug. Upon completion of the installation of the end plug on the housing, a vacuum is applied to the pipe 26 by suitable means (not shown) to withdraw substantially all gas from the interior of the housing.

As shown in FIGURE 10, when the desired vacuum condition is obtained within the housing 16 the pipe 26 is pinched and Welded closed as at 26b to complete the sealing of the wires 12 within the housing 16. To provide an improved vacuum within the housing 16, the housing may be disposed within a suitable conventional heater The resultant housed bundle comprises a billet 31 which is next subjected to a hot forming process to reduce the diameter thereof in one or more passes. As illustrated in FIGURE 11, the billet 31 maybe reduced in diameter by a hot extrusion step wherein the billet is forced through heated extrusion dies 32 by a suitable pressure device 33. It is desirable that the billet 31 be preheated to a preselected suitable temperature and suitably lubricated for facilitated extrusion in this step. The rate and pressure of the extrusion is preselected to provide optimum diametric reduction of the billet in conformity with the nature of the materials involved. In the event that a second extrusion step is employed, the opposite ends 34 of the reduced diameter billet 35 are trimmed (see FIGURE 12) as by suitable cutters 36. Any nonuniform extruded end portions of the billet as deter mined by observation thereof may be included in the ends 34 so cut from the billet. The trimmed billet 35 is then divided into a plurality of short lengths 37, as shown in FIGURE 13, by suitable means such as cutting wheels 38 Each of the short length billets 37 is then provided with a nose plug 39 and a tail plug 40 as by welding as llustrated in FIGURE 14. The short length billet 37 is then reheated and passed through heated extrusion dies 41 (see FIGURE 15) for further diametric constriction thereof to a final formed billet 42.

As indicated briefly above, the hot forming of the billet 31 may be effected by hot rolling the billet in lieu of the extrusion thereof. Thus, as shown in FIGURE 16, the billet 31 may be suitably heated and passed between suitable rolls 43. The billet 31 may be firstly hot formed by the extrusion step illustrated in FIGURE 11 and subsequent hot forming effected by hot rolling as desired. The rolls 43 are preferably arranged to produce a hot forming constriction of the billet wherein the elements therein are maintained in a substantially circular crosssectional configuration.

Subsequent to the hot forming steps discussed above, as shown in FIGURE 17, the resultant final formed billet 42 is drawn through a suitable conventional drawing die 44 by a suitable conventional drawing device 45. The billet may be successively drawn down to smaller and smaller diameters by means of successively smaller dies 44 to produce the final desired small diameter filaments. Annealing may be effected between the successive drawing steps in conformity with the requirements of the metal of which the filaments are formed. The cold drawing of the billet may be conducted suitably to develop texture in the filaments and to work-harden the filaments for providing improved mechanical properties thereto.

Where the hot rolling steps are employed, the final cold drawing of the billet may be dispensed with, such as where the physical characteristics provided by the cold drawing are not required. Thus, the hot rolling steps may be continued with successively smaller rolls 43 providing the desired ultimate constrictive deforming of the billet whereby the filaments may be made to have the desired diameter of approximately 12 microns or less.

The filaments are released from the final constricted billet 46 by suitable means such as selective chemical attack of the sheathing 15 and can 16. Thus, as shown in FIGURE 18, the final billet 46 may be disposed within a tank 47 holding a suitable acid 48 to dissolve the sheathing and can material. Obviously, other methods of removal of the can and sheathing material may be employed; illustratively, the sheathing and can material may be removed by electromechanical dissolution, selective oxidation, mechanical removal, etc. In the final tow of filaments 11, as illustrated in FIGURE 19, the filaments have an extremely small diameter, for example, down to approximately .0005 inch or 12 microns or less. Where the filaments are formed by utilizing the hot extrusion process with subsequent cold drawing, the tow filaments may have a length of up to 50,000 feet or more, and where the tow filaments are formed by the hot rolling process, the length may be up to 300,000 feet or more.

More specifically, the wire 12 of which the filaments are ultimately formed may comprise a metal wire formed of a suitable material, one example being 304 stainless steel. The sheathing may comprise copper or Monel meta Alternatively, the sheathing may comprise an oxide coating deposit on the wire 12. One example of material of which can 16 may be formed is mild steel. Thus, in the final step, the mild steel can and the copper, or Monel, sheathing materials may be removed from filaments such as stainless steel filaments by use of a nitric acid fluid 48.

One example of the formation of stainless steel filaments comprehended by the invention is as follows. The wires 12 may comprise 304 stainless steel Wires .250 inch in diameter and 18 inches long. The sheath may comprise a Monel 400 tube having a .293 inch outside diameter, a .253 inch inside diameter, and a length of 18 inches. The can 16 may be formed of mild steel having a 5.95 inch outside diameter, a 5.25 inch inside diameter, and an overall length of 22 inches. The nose plug 23 may comprise a 45 degree angle plug. Two hundred sixtyeight (268) of the sheathed wires may be placed in the can 16, and the can evacuated to less than .1 n of mercury at 800 degrees F. and sealed off. The billet may then be heat treated at 1800 degrees F. for six hours in a graphite container. The extrusion dies 32 may be preheated to 900 degrees F., and have an internal diameter of 2.925 inches, whereby an extrusion ratio of 4.3x in 6 area is obtained. The billet 31 may be suitably lubricated, and the ram 33 operated at a speed of approximately 500 inches per minute under a pressure 1340 tons upset, 1200 tons running.

The extrusion 35 may be water quenched immediately upon extrusion, and cut into 10 inch lengths. A new 45 degree angle nose plug and a .5 inch end plug may be welded to the opposite ends of the short length billet 37 for a second extrusion operation. The extrusion die may be preheated to 900 degrees F., and have an internal diameter of .625 inch providing an extrusion ratio of 22.8 in area. The billet 37 may be preheated at a temperature of 1800 degrees F. for three hours in a graphite container. The extrusion speed may be inches per minute at a pressure 590 tons upset, 560 tons running. The extruded billets 42 may be water quenched immediately after this second extrusion.

The billet 42 may then be cold drawn in four passes to a total reduction of approximately 60%, each pass providing a reduction of approximately 20% of the crosssectional area. Between the 60% reductions the drawn billet may be annealed at a temperature of approximately 1700 degrees F. for two seconds per .001 inch of wire diameter. The final diameter is approximately .016 inch producing filaments approximately .0007 inch in diameter.

The can 16 and sheath 15 material may be removed by means of nitric acid in tank 47.

The resultant filaments formed as above have an average ultimate tensile strength, cold worked, of approximately 250,000 p.s.i. with an average elongation, cold worked, of approximately 2.1%. The filaments have an average ultimate tensile strength annealed of approximately 109,000 p.s.i. with the average elongation annealed being approximately 11%.

Another example of the forming of fine filaments by the present invention comprises the following. The wires 12 may comprise 304 stainless steel wires .080 inch in diameter and the sheath 15 may comprise a Monel 400 tube having a .097 inch outside diameter, a .085 inch inside diameter, and a length of 20 feet. The can 16 may be formed of mild steel having a 1.970 inch outside diameter, a 1.740 inch inside diameter, and an overall length of 6 inches. The nose plug 23 may comprise a 45 degree angle plug. Lengths of the stainless steel wire may be sheathed with the Monel tube and drawing through a .091 inch diameter die to facilitate mating. After strainghtening the sheathed wire may be cut into 3 inch lengths for packing in the can. Two hundred forty-two (242) of the sheathed wires may be placed in the can 16, and the can evacuated to less than .1/1. of mercury at 800 degrees F. and sealed off. The billet may then be heat treated at 1800 degrees F. for two hours in a graphite container. The extrusion dies 32 may be preheated to 900 degrees F. and have an internal diameter of .500 inch, whereby an extrusion ratio of 16X in area is obtained. The billet 31 may be suitably lubricated, and the ram 33 operated at a speed of approximately 65 inches per minute under a pressure of 272 tons upset, 260 tons running.

The extruded billet 31 may be then cold drawn in successive passes to a final diameter of .008 inch. Between steps of 60% reduction in area the drawn billet may be annealed at a temperature of approximately 1700 degrees F. for two sheconds per .001 inch of wire diameter.

The can 16 and sheath 15 material may be removed by means of nitric acid in tank 47. The final diameter of the filaments 11 as formed above is approximately .00034 inch.

As indicated briefly above, the present invention comprehends the forming of tubular filaments by the process described above for forming fine solid wire filaments. As illustrated in FIGURES 20 through 24, in forming tubular filaments, the starting elongated element comprises the metal tube 14 which may be firstly filled with a solid wire 49 and then enclosed in a suitable sheath 50. Each of the wire 49 and the sheath 50 are formed of a material having physical characteristics differing from those of the tubes 14 to permit separation of the wire 49 and sheath 50 material when desired. Illustratively, the tube 14 may be formed of 304 stainless steel, the wire 49 may be formed of copper, and the sheath 50 may be formed of Monel 400 metal. As shown in FIG- URE 22, the tube, wire and sheath assembly may be firstly drawn to constrict the tube onto the wire 49 and the sheath onto the tube 14 in intimate contact. Illustratively, the resultant composite 51 may have an outside diameter of .100 inch with the tube having an outside diameter of .085 inch, and the Wire having an outside diameter of .045 inch. The composites 51 may be cut to three inch lengths, and sixty-one such lengths may be installed in a mild steel can 52 having an outside diameter of 1.063 inches and an inside diameter of .920 inch, whereby the extrusion ratio may be approximately 16 in area. The billet temperature may be 1800 degrees F. and the extrusion pressures may be 70 tons upset and 65 tons running.

The resultant extruded billet may then be cold drawn to approximately .172 inch outer diameter. The resultant tubular filaments 13 may then be released after cutting the composite drawn billet into suitable lengths in the manner illustrated in FIGURE 18. The resultant tubular filaments 13 are uniform in cross-sectional dimension within deviation from the mean and have an average transverse dimension (i.e., between vertices) of .015 inch.

Thus, the present invention comprehends an improved method of forming both solid and tubular filaments permitting facilitated and economical manufacture, while yet the filaments produced thereby have uniform crosssection and extremely long lengths.

While we have shown and described certain embodiments of our invention, it is to be understood that it is capable of many modifications. Changes, therefore, in the construction and arrangement may be made without departing from the spirit and scope of the invention as defined in the appended claims.

We claim:

1. A filament formed of metallic material and having a surface portion having a trace of a removed surrounding matrix material, said filament having a texture developed by successive hot and cold working thereof.

2. The filament according to claim 1 wherein said filament has a diameter down to 12 microns or less.

3. The filament according to claim 1 wherein said filament is tubular.

4. The filament according to claim 3 wherein the inner surface of the tubular filament has a trace amount of removed wire material therein.

5. The filament according to claim 3 having a generally hexagonal outer cross-section.

6. The filament according to claim 1 having a length of over approximately 50,000 feet.

7. The filament according to claim 1 which is workhardened.

8. The filament according to claim 1 wherein said metallic material is stainless steel.

9. The filament according to claim 1 wherein said matrix comprises Monel metal.

10. The filament according to claim 1 wherein said filaments has a diameter of under 15 microns.

11. The filament according to claim 1 wherein said filament surface has a trace amount of oxide thereon.

12. The filament according to claim 1 having a tensile strength of at least 250,000 p.s.i.

13. The filament according to claim 1 which is annealed.

14. The filament according to claim 1 wherein said outer surface of said filament is unburnished.

References Cited UNITED STATES PATENTS 2,050,298 8/1936 Everett 29-180 X 2,215,477 9/1940 Pipkin 29-193 2,499,977 3/1950 Scott 148-4 2,619,438 11/1952 Varian et al. 29-423 X 2,842,440 7/1958 Nachtrnan et al. 29-183.5 X 3,131,469 5/1964 Glaze 29-191 X 3,189,990 6/1965 Metzger 29-423 3,222,144 12/1965 Davenport 29-191 3,239,919 3/1966 Levi 29-423 X 3,370,347 2/1968 Garwin et al. 29-599 3,379,000 4/1968 Webber et a1 29-193 X HYLAND BIZOT, Primary Examiner E. L. WEISE, Assistant Examiner U.S. Cl. X.R. 29-193, 196.6 

